Resetting the die ejection mechanism
The reset mechanism of a die-casting mold is crucial for ensuring continuous and stable mold operation. Its function is to accurately and quickly return all ejection mechanism components (such as the ejector rod, ejector tube, and ejector plate) to their initial positions after each die-casting, preparing for the next die-casting cycle. The design quality of the reset mechanism directly impacts mold production efficiency and the quality of die-castings. Inaccurate reset can prevent the mold from closing properly, or even damage mold components or the die-casting. Therefore, the reliability, accuracy, and efficiency of the reset mechanism must be fully considered when designing the ejection mechanism.
Common methods for resetting the ejection mechanism of a die-casting mold include reset spring reset, reset rod reset, and hydraulic reset. Reset spring reset utilizes the elastic force of a spring installed on the ejector rod mounting plate or the ejector plate to reset the ejection mechanism. This method is simple in structure and low in cost, making it suitable for applications with low ejection force and low reset requirements. Reset springs are typically cylindrical helical compression springs, the specifications of which are determined by the weight of the ejection mechanism and the required reset force. The spring is generally pre-compressed by 15%-20% of its free length to ensure sufficient reset force. However, reset springs are prone to fatigue failure over long-term use, resulting in insufficient reset force, and therefore require regular inspection and replacement.
Reset rods are installed on the ejector plate. The ejector mechanism is reset using the thrust of the fixed mold against the rods during mold closing. This method provides accurate and reliable reset, making it suitable for most die-casting molds, especially those requiring high reset accuracy. Four reset rods are typically located at the four corners of the ejector plate. Their length must be precisely calculated to ensure that, when the mold is closed, their end faces contact the parting surface of the fixed mold, allowing the ejector plate to return to its initial position. The reset rods and ejector plate utilize an H7/m6 transition fit, ensuring they move with the ejector plate while preventing wobbling caused by excessive clearance. The reset rods are typically made of 45 steel, tempered to a hardness of HB220-250 to ensure strength and wear resistance.
Hydraulic reset utilizes a hydraulic cylinder to drive the ejection mechanism. This method offers high reset force and adjustable speed, making it suitable for large, complex die-casting molds, particularly those with heavy ejection mechanisms or long reset strokes. The hydraulic reset system, consisting of a hydraulic cylinder, tubing, and a reversing valve, resets the ejection mechanism by controlling the expansion and contraction of the hydraulic cylinder. The advantages of hydraulic reset are uniform reset force and smooth operation. The reset speed and force can be controlled by adjusting the pressure and flow of the hydraulic system to meet varying operating requirements. However, the hydraulic reset system’s complex structure, high cost, and the need for regular maintenance of hydraulic components have limited its application in small and medium-sized die-casting molds.
Precision control of the ejection mechanism’s reset is crucial to the die-casting mold’s design. Reset accuracy is typically required to be within 0.02-0.05mm to ensure that all ejection mechanism components return accurately to their initial positions and avoid interference with other mold components. To improve reset accuracy, the following measures can be taken: First, rationally arrange the reset rod or reset spring to ensure uniform force distribution and prevent deflection of the ejection mechanism during reset. Second, improve the machining accuracy of the mating parts—such as the reset rod and guide sleeve, and the ejector plate and guide post—to reduce clearance. Third, incorporate limit devices, such as stoppers and blocks, into the reset mechanism to precisely control the ejection mechanism’s reset position. Furthermore, during mold assembly, the reset mechanism requires careful adjustment to ensure coordinated movement of all reset components and accurate reset positions.
The reset design of the ejector mechanism in a die-casting mold also needs to consider coordination with other mold operations. In molds with components such as core pulling mechanisms and inclined guide pins, the reset action must be coordinated with the core pulling and mold opening processes. Typically, the sequence is either reset first, then core pulling, or core pulling first, then reset. The specific sequence depends on the structural characteristics of the die-casting part and the operating principle of the mold. For example, for molds with inboard core pulling, the ejector mechanism must be reset before core pulling to avoid interference with components such as the ejector pin. For molds with outboard core pulling, core pulling can be performed first, followed by reset, to reduce the overall mold size. Furthermore, the reset mechanism design must facilitate mold commissioning and maintenance, and reset components must be interchangeable to allow for quick replacement if damaged. With the continuous advancement of die-casting technology, reset mechanism design is also undergoing continuous innovation. The use of advanced technologies such as electronic sensors to monitor and control the reset position in real time can further improve reset accuracy and reliability, providing a strong guarantee for efficient and stable mold operation.
